Water purification technology is rapidly becoming an essential aspect of modern life as conventional water resources become increasingly scarce, municipal distribution systems for potable water deteriorate with age, and increased water usage depletes wells and reservoirs, causing saline water contamination. Additionally, further contamination of water sources is occurring from a variety of activities, which include, for example, intensive agriculture, gasoline additives, and heavy toxic metals. These issues are leading to increasing and objectionable levels of germs, bacteria, salts, MTBE, chlorates, perchlorates, arsenic, mercury, and even the chemicals used to disinfect potable water, in the water system.
Furthermore, even though almost three fourths of the earth is covered by oceans, fresh water resources are limited to some 3% of all planetary water and they are becoming scarcer as a result of population growth and global warming. Approximately 69% of all fresh water is held in ice caps and glaciers which, with increased global melting become unrecoverable, so less than 1% is actually available and most of that (over 90%) is ground water in aquifers that are being progressively contaminated by human activities and saline incursions. Thus, there is an urgent need for technology that can turn saline water, including seawater and brine, into fresh water, while removing a broad range of contaminants.
Conventional desalination and water treatment technologies, such as reverse osmosis (RO) filtration thermal distillation systems like multiple-effect distillation (MED), multiple-stage flash distillation (MSF), or vapor compression distillation (VC) are rarely able to handle the diverse range of water contaminants found in saline environments. Additionally, even though they are commercially available, they often require multiple treatment stages or combination of various technologies to achieve acceptable water quality. RO systems suffer from the requirement of high-water pressures as the saline content increases which render them increasingly expensive in commercial desalination, and they commonly waste more than 30% of the incoming feed water, making them progressively less attractive when water is scarce. Less conventional technologies, such as ultraviolet (UV) light irradiation or ozone treatment, can be effective against viruses and bacteria, but seldom remove other contaminants, such as dissolved gases, salts, hydrocarbons, and insoluble solids. Additionally, most distillation technologies, while they may be superior at removing a subset of contaminants are frequently unable to handle all types of contaminants.
Because commercial desalination plants are normally complex engineering projects that require one to three years of construction, they normally are capital intensive and difficult to move from one place to another. Their complexity and reliance on multiple technologies also make them prone to high maintenance costs. Thus, because RO plants are designed to operate continuously under steady pressure and flow conditions, large pressure fluctuations or power interruptions can damage the membranes, which are expensive to replace; that technology requires extensive pre-treatment of the incoming feed water to prevent fouling of the RO membrane. Thermal distillation systems frequently rely on vacuum to increase water recovery by extracting increasing steam with a given amount of thermal energy; however, vacuum systems in large-scale systems are troublesome because of leaks and require mechanical reinforcement. Thermal systems also rely on heat exchangers to recover some of the heat of condensation, but heat exchangers are prone to fouling and scale formation and require frequent maintenance.
Accordingly, sophisticated distillation systems that are continuous and self-cleaning, that resist corrosion, that are portable and compact and recover a major fraction of the input water, and that are relatively inexpensive and low-maintenance appear as the best long-term option to resolve increasing water contamination problems and water scarcity, worldwide.